Composition, Properties and Uses of Polymer Questions in English

(A) The polydispersity index $(PDI)$ is defined as the ratio of weight average molecular weight to number average molecular weight.
$PDI = \frac{\bar{M}_w}{\bar{M}_n}$
Given:
$\bar{M}_w = 60000$
$\bar{M}_n = 40000$
$PDI = \frac{60000}{40000} = 1.5$
Since $1.5 > 1$,the polydispersity index of the polymer is $>1$.

(B) The weight average molecular mass is calculated using the formula: $\bar{M}_w = \frac{\sum n_i M_i^2}{\sum n_i M_i}$
Given:
$n_1 = 3, M_1 = 1000$
$n_2 = 3, M_2 = 500$
$n_3 = 4, M_3 = 200$
Numerator: $(3 \times 1000^2) + (3 \times 500^2) + (4 \times 200^2) = 3,000,000 + 750,000 + 160,000 = 3,910,000$
Denominator: $(3 \times 1000) + (3 \times 500) + (4 \times 200) = 3000 + 1500 + 800 = 5300$
$\bar{M}_w = \frac{3,910,000}{5300} \approx 737.7$

(B) The ratio of weight average molecular weight to the number average molecular weight is defined as the poly dispersity index $(PDI)$.
$PDI = \frac{\bar{M}_w}{\bar{M}_n}$
where,
$\bar{M}_w = \text{weight average molecular weight}$
$\bar{M}_n = \text{number average molecular weight}$
For natural monodispersed polymers,$PDI = 1$,whereas for synthetic polymers,$PDI > 1$.

(D) Orlon is also known as polyacrylonitrile $(PAN)$.
The monomer used for the preparation of orlon is acrylonitrile,which has the chemical formula $CH_2=CH-CN$.